Modern image formats
WebP and AVIF carry the same picture in a fraction of the bytes. What the trade-offs are, and the markup that keeps a fallback for old browsers.
What it is
This check looks at the images a page actually loaded and counts the ones still served as PNG or JPEG where a modern format would do the same job smaller.
WebP and AVIF are both lossy-or-lossless formats with substantially better compression than JPEG and PNG. WebP is supported everywhere that matters and is the safe default; AVIF compresses harder still and encodes more slowly.
Why it matters
Images are usually the largest thing on a page by bytes, which makes them the largest single lever on load time — and the one that requires no architectural change, only re-encoding.
It also lands directly on Largest Contentful Paint, because the LCP element is so often a hero image. Halving that file's size moves the metric Google actually measures, on the element that defines it.
How to fix it
with a reference doc<picture>
<source srcset="photo.avif" type="image/avif">
<source srcset="photo.webp" type="image/webp">
<img src="photo.jpg" alt="…" width="1200" height="800">
</picture>// next/image negotiates the format per request; no <picture> needed
import Image from "next/image";
<Image src="/photo.jpg" alt="…" width={1200} height={800} />Related checks
4This is one of the 75 checks the scanner runs. See what we check for the full list, every severity weight, and how the score is computed from them.